Expandable Vertebral Prosthesis

ABSTRACT

The present invention relates to an expandable prosthetic implant device for engagement between vertebrae generally comprising an inner member, outer member, and gear member positioned coaxial with respect to each other such that the inner and outer members are moveable relative to each other along an axis. The gear member is axially fixed to the outer member and freely rotatable with respect to the outer member and the gear member threadedly engages a threaded portion of the inner member to translate inner member along the axis. The implant is configured to engage the vertebrae in a predetermined alignment and the gear member includes gear teeth exposed to the exterior and configured to be accessible by a tool member at a plurality of angular positions around the perimeter of the implant device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The application claims priority to U.S. application Ser. No. 11/110,844filed on Apr. 10, 2005 which is incorporated herein in its entirety byreference.

FIELD OF THE INVENTION

The present invention relates to a device to support the spine afterremoval of at least a part of a vertebra.

BACKGROUND OF THE INVENTION

When a vertebra is damaged or diseased, surgery may be used to replacethe vertebra or a portion thereof with a prosthetic device to restorespinal column support. For example, vertebral body replacement iscommonly required in the treatment of vertebral fracture, tumor, orinfection.

In recent years, several artificial materials and implants have beendeveloped to replace the vertebral body, such as, for example, titaniumcages, ceramic, ceramic/glass, plastic or PEEK, and carbon fiberspacers. Recently, various expandable prosthetics or expandable cageshave been developed and used for vertebral body replacement. Theexpandable prosthetic devices are generally adjustable to the size ofthe cavity created by a corpectomy procedure and typically are at leastpartially hollow to accommodate bone cement or bone fragments tofacilitate fusion in vivo. Some expandable prosthesis may be adjustedprior to insertion into the cavity, while others may be adjusted insitu. One advantage of the vertebral body replacement using anexpandable prosthetic device that is adjustable in situ is that it iseasy to place or insert because it permits an optimal, tight fit andcorrection of the deformity by in vivo expansion of the device. Someother advantages offered by an expandable prosthetic device are thatthey can facilitate distraction across the resected vertebral defect forcorrection of the deformity, and allow immediate load bearing aftercorpectomy.

Instrumentation and specialized tools for insertion of a vertebralimplant is one important design parameter to consider when designing avertebral prosthesis. Spinal surgery procedures can present severalchallenges because of the small clearances around the prosthetic when itis being inserted into position. Another important design considerationincludes the ability of the device to accommodate various surgicalapproaches for insertion of the vertebral implant.

SUMMARY OF THE INVENTION

The present invention relates to an expandable prosthetic implant devicefor engagement between vertebrae generally comprising an inner member,outer member, and gear member positioned coaxial with respect to eachother such that the inner and outer members are moveable relative toeach other along an axis. The inner member has a hollow interior portionand a threaded external portion and includes a first end portionconfigured to engage a first vertebral body. The outer member has ahollow interior portion configured to receive the inner member andincludes a second end portion configured to engage a second vertebralbody. The gear member is axially fixed to the outer member and freelyrotatable with respect to the outer member and the gear memberthreadedly engages the threaded portion of the inner member.

The implant is configured to engage the vertebrae such that first andsecond end portions are oriented in a predetermined alignment withrespect to the first and second vertebral bodies. The gear memberincludes gear teeth extending around the perimeter of the gear memberand the gear teeth are exposed to the exterior and configured to beaccessible by a tool member at a plurality of angular positions aroundthe perimeter.

In one embodiment, the outer member includes a plurality of toollocation holes for receiving a portion of a tool member therein tofacilitate insertion, alignment and engagement of the tool member withthe gear teeth. In another variation, the outer member includes aresiliently deformable portion for receiving the gear member thereon. Inyet another embodiment, the inner member, outer member, and gear membermay be made of a PEEK plastic material. In another embodiment, thedevice also includes a locking member for fixing the inner member withrespect to the outer member.

In one embodiment, the inner member is rotationally fixed with respectto the outer member. In one variation, the inner member includes a slotand a pin extends radially inward from the outer member to engage theslot to prevent rotational movement of the inner member with respect tothe outer member.

In another embodiment, the first end portion may comprise a first platehaving a generally oblong shape when viewed perpendicular to thelongitudinal axis, the first plate extending a width distance along along axis and a depth distance along a short axis, wherein the widthdistance is larger than the depth distance. Similarly, in anotherembodiment, the second end portion may comprise a second plate having agenerally oblong shape when viewed perpendicular to the longitudinalaxis, the second plate extending a width distance along a long axis anda depth distance along a short axis, wherein the width distance islarger than the depth distance. In one variation, the first and secondend plates include at least one bone engaging member extendinglongitudinally from the end plates. The bone engaging members maycomprise metal spikes.

In another variation, end portions have a thickness in the longitudinaldirection and the thickness is variable in the anterior-posteriordirection along the short axis. In one embodiment, the thickness variesgradually in the anterior-posterior direction such that the end portiondefines a general wedge-shaped profile. In another embodiment, the endportion extends in the anterior-posterior direction from an anteriorside to a posterior side and the first end portion has a first thicknessat an anterior side and a second thickness at a posterior side, whereinthe first thickness is greater than the second thickness. In yet anotherembodiment, the end portion includes a bone engaging surface and a planetangent to the bone engaging surface intersects a plane normal to thelongitudinal axis at a first angle. In one variation, the angle isbetween about −16 degrees and about 16 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood with reference to theembodiments thereof illustrated in the attached drawing figures, inwhich:

FIG. 1 is a perspective view of a prosthetic device in accordance withan embodiment of the invention;

FIG. 2 is an exploded view of the prosthetic device of FIG. 1;

FIG. 3 is a cross-sectional view of the prosthetic device of FIG. 1taken along line 3-3 of FIG. 1;

FIG. 4 is perspective view of an embodiment of an inner member of theprosthetic device of FIG. 1;

FIG. 5 is perspective view of an embodiment of an outer member of theprosthetic device of FIG. 1;

FIG. 6 is an end view of the prosthetic device of FIG. 1;

FIG. 7 is an elevated side view of one embodiment of a gear member ofthe prosthetic device of FIG. 1;

FIG. 8 is an end view of the gear member of FIG. 7;

FIG. 9 is a cross-sectional view of the gear member of FIGS. 7 and 8taken along line 9-9 of FIG. 8;

FIG. 10 is a perspective of one embodiment of a tool according to thepresent invention;

FIG. 11 is a perspective view of the tool of FIG. 10 shown engaging anembodiment of an expandable prosthetic device according to theinvention;

FIG. 12 is a partial cross-sectional view of the combination of FIG. 11;

FIG. 13 is a cross-sectional view of another embodiment of an outermember according to the invention; and

FIGS. 14-25 depict various alternate embodiments of expandableprosthetic devices according to the present invention.

Throughout the drawing figures, it should be understood that likenumerals refer to like features and structures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the invention will now be described withreference to the attached drawing figures. The following detaileddescription of the invention is not intended to be illustrative of allembodiments. In describing preferred embodiments of the presentinvention, specific terminology is employed for the sake of clarity.However, the invention is not intended to be limited to the specificterminology so selected. It is to be understood that each specificelement includes all technical equivalents that operate in a similarmanner to accomplish a similar purpose.

Referring to FIGS. 1-9, one embodiment of an expandable vertebralprosthetic device 10 is shown. Prosthesis 10 generally comprises aninner member 12 which may be telescopingly received within an outermember 14. The prosthesis 10 further comprises a gear member 16generally configured to effect translation of inner member 12 withrespect to outer member 14 and cause expansion of prosthesis 10. Innermember 12, outer member 14, and gear member 16 are centered along alongitudinal axis 18 and define a hollow interior portion which may befilled with bone material, bone growth factors, bone morphogenicproteins, or other materials for encouraging bone growth, blood vesselgrowth or growth of other tissue through the many apertures in thedevice. In one embodiment, members 12, 14, and 16 are made of apolyether ether ketone (PEEK) plastic material. Several known advantagesof PEEK plastic material include that it is radiolucent and may be moreeasily sterilized than other plastics. In alternate embodiments, members12, 14, and 16 may be made of a biologically inert metal alloy or othersuitable materials.

Referring to FIGS. 1-4, inner member 12 has an endplate 20 at a distalend 22 connected to a generally cylindrical body 24 at a proximal end 26and generally defines a hollow interior portion extending axiallytherethrough. Body 24 of inner member 12 generally comprises a wall 27with an inner surface 28 and an outer surface 30 and at least part ofouter surface 30 includes external threads 32. Outer diameter 34 of body24 is dimensioned to be cooperatively received within outer member 14.

Outer member 14 has an endplate 40 at a proximal end 42 connected to agenerally cylindrical body 44 at a distal end 46 and generally defines ahollow interior portion extending axially therethrough. Body 44 of outermember 14 generally comprises a wall 47 with an inner surface 48 and anouter surface 50. Inner diameter 52 of body 44 is dimensioned tocooperatively receive body 24 of inner member 12 within outer member 14.In this regard, inner diameter 52 of body 44 is greater than outerdiameter 34 of body 24 of inner member 12. As shown in FIG. 1, outermember 14 may include one or more openings 53 to permit bone ingrowth.According to one embodiment, a lip 54 is formed around the exterior ofthe distal end 46 of body 44 and is configured to cooperatively fit witha portion of gear member 16. A plurality of relief spaces or slots 56extending through wall 47 are angularly spaced around body 44 adjacentdistal end 46 to facilitate a snapping engagement of lip 54 with gearmember 16. In this regard, slots 56 allow distal end 46 to deformslightly and contract in the radial direction to accommodate gear member16 to snap on to lip 54.

As best seen in FIGS. 2-4, in one embodiment of a prosthetic device 10,inner member 12 includes a plurality of longitudinal slots 36 extendingradially through wall 27. Slots 36 are angularly spaced around body 24and extend longitudinally along wall 27. When inner member 12 isassembled within outer member 14, slots 36 are configured to engage atleast one pin 38 protruding radially inward from the inner surface 48 ofouter member 14 to prevent rotational movement of inner member 12 withrespect to outer member 14. In this regard, pin 38 may extend into oneof slots 36 and may ride within one of the longitudinal slots 36 duringexpansion of the prosthetic device 10 to prevent rotation of innermember 12 with respect to outer member 14. In addition, pin 38 mayprevent inner member 12 from expanding or translating along axis 18beyond a predetermined distance when pin 38 bottoms out or contacts theproximal end 39 of the slot in which it is engaged.

Referring to FIGS. 7-9, gear member 16 comprises a generally hollow body60 extending from a distal end 61 to a proximal end 63 with a helicalthread 62 along at least part of an inner wall 64 and an array of gearteeth 66 along a portion of the exterior wall 68. Gear member 16 isgenerally configured to rotatably connect to distal end 46 of outermember 14 and internal helical thread 62 is configured to engageexternal threads 32 of inner member 12 to cause translation of innermember 12 with respect to outer member 14. In one embodiment, gearmember 16 includes a cylindrical cutout feature 65 extending around theinner wall 64 to cooperatively receive lip 54 of outer member 14. Inthis regard, gear member 16 may rotate freely with respect to outermember 14 while being retained from longitudinal and lateral movement.In this regard, the aforementioned snap-on feature allows for the designand manufacture of a relatively thin walled outer member 14 tofacilitate the creation of a larger inner diameter of outer gear member16 and inner member 12. As a result, more bone growth stimulatingmaterial may be packed into the prosthetic device 10. Also, by creatinga larger inner diameter of gear member 16 and inner member 12, a largerthread size for external thread 32 and internal thread 62 may beutilized to provide greater mechanical strength.

Referring to FIG. 7, gear teeth 66 are positioned at an angle withrespect to the proximal end 63 and extend around the entire periphery ofa portion of exterior wall 68 to form a general frusto-conical gearteeth surface adjacent the proximal end 63. The outer-most externaldiameter 67 of gear member 16 is sized to be the same as or slightlysmaller than the smallest outer diameter of endplates 20, 40. In thisregard, when prosthetic device 10 is viewed from the end in a planeperpendicular to longitudinal axis 18, as shown in FIG. 6, gear member16 does not protrude radially outward from beyond the perimeter ofendplates 20, 40. In one embodiment, the outer-most diameter of gearmember 16 is substantially the same size as the smallest outer diameterof endplates 20, 40. As shown in FIG. 7, in one embodiment gear teeth 66extend a width 69 in a generally radial direction and generally extendradially outward to the outer diameter of gear member 16. In thisregard, teeth 66 may be designed to have a width 69 to accommodate theexpected gear forces given the particular bevel gear ratio, types ofmaterial used, and desired overall inner diameter of prosthetic device10. One skilled in the art will appreciate that the larger the outerdiameter to which teeth 66 radially extend, the larger that teeth 66 maybe designed while still maintaining the same gear ratio. In this regard,when teeth 66 are made larger, they generally have a better mechanicalstrength. Also, the ability to design larger, wider, and stronger teeth66 is advantageous for embodiments wherein prosthesis 10 is made ofPEEK, other plastic, or other non-metallic materials that may have lessmechanical strength than, for instance, titanium. Furthermore, asdescribed in one embodiment, because the outer-most diameter of gearmember 16 may be as large as the smallest outer diameter of endplates20, 40, and teeth 66 extend radially to the outer-most diameter of gearmember 16, a larger inner diameter of gear member 16 may be manufacturedwithout compromising mechanical gear strength. As a result, a largeroverall inner diameter of prosthetic device 10 may be accommodated whichallows the packing of more bone material therein and facilitates bonefusion once prosthetic 10 is implanted.

As seen in FIGS. 1 and 2, in one embodiment teeth 66 are substantiallyexposed to the exterior of prosthetic device 10. Because teeth 66 areexposed around the periphery, less material is needed to cover up theexposed teeth, which generally makes the prosthetic 10 lighter andeasier to manufacture than prior art devices that require covering thegear teeth. In addition, the gear member 16 is more easily visible by asurgeon and more readily accessible by a rotation tool than devices thathide or cover gear teeth. As discussed in more detail below, such afeature allows, inter alia, a tool to engage teeth 66 at a multitude ofangular positions around the periphery of outer member 14 to provide asurgeon with various surgical options for insertion of prosthetic device10. Furthermore, the snap-on assembly feature of gear member 16 allowsfor the manufacture of thinner walled parts without sacrificingmechanical strength. As a result, prosthesis 10 is able to have a largerinternal diameter which allows more space for bone-packing material.

As shown in FIGS. 10-12, prosthesis 10 may be expanded by a tool 70 thatincludes a bevel gear 72 at its distal end. Tool 70 extends along a toolaxis 74 and in operation tool 70 is configured to engage prostheticdevice 10 such that tool axis 74 is generally perpendicular tolongitudinal axis 18. Bevel gear 72 is configured to engage teeth 66 ofgear member 16 such that when bevel gear 72 is rotated about the axis ofthe tool, gear member 16 of prosthetic 10 is rotated about longitudinalaxis 18 and inner member 12 translates along longitudinal axis 18 toexpand prosthesis 10. In one embodiment, tool 70 may include a centralshaft 76 having a threaded distal tip portion 78 that extends distallybeyond bevel gear 72 to facilitate location and mounting of tool 70 withprosthetic 10. Threaded distal tip portion 78 may be configured toextend radially through a tool location hole 80 in outer member 14 andthreadedly engage a threaded hole 81 located on the inner surface 48 ofwall 47 positioned diametrically opposite hole 80 to fix the centralshaft 76 of tool 70 to outer member 14. Once central shaft 76 is fixedto outer member 14, bevel gear 72 may rotate with respect to centralshaft 76 to effect rotation of gear member 16 and translation of innermember 12.

Referring again to FIGS. 2 and 4, in one embodiment of prosthetic device10 a plurality of mounting features or tool location holes 80, 82, 84are provided along the outer surface 50 of outer member 14. Toollocation holes 80, 82, 84 may be spaced around outer surface 50 in apredetermined arrangement to allow insertion of prosthetic device 10utilizing different surgical approaches. For example, one skilled in theart will appreciate that holes 80, 82, 84 may be arranged to permitinsertion through a lateral approach, anterolateral approach, or ananterior approach. As shown in FIG. 4, tool location hole 80 isangularly located or positioned on wall 47 toward the front ofprosthetic 10 or toward the short end of end plates 20, 40 to facilitateinsertion of prosthetic device 10 into a patient via an anteriorapproach. Tool location hole 82 may be angularly located or positionedon wall 47 to be toward the side of prosthetic 10 or toward the long endof end plates 20, 40 to facilitate insertion of prosthetic device 10into a patient via a lateral approach. In addition, a third toollocation hole 84 may be angularly located or positioned to be betweenlocation holes 80 and 82 to facilitate insertion of prosthetic device 10through an anterolateral approach. As described previously, for eachlocation hole 80, 82, 84, a corresponding threaded hole 81, 83, 85 maybe formed on the inner surface 48 of wall 47 and positioneddiametrically opposite the corresponding tool location hole to permitthe threaded engagement of distal tip portion 78 of tool 70.

As best seen in FIGS. 1, 2 and 4, a locking member 120 may be providedto substantially restrict all relative movement between inner member 12and outer member 14, when, for example, the desired expansion of theprosthetic device 10 has been obtained. In one embodiment of the lockingmember 120 according to the invention, a portion of locking member mayprotrude radially inward from the outer member 14 to engage the externalsurface 30 or thread 32 of inner member 12 and lock or fix inner member12 to outer member 14 by friction and/or deformation of external threads32. An internal locking screw 121 may be provided internal to lockingmember 120 to translate the locking member radially inward when thescrew 121 is rotated. Screw 121 may be provided with a hexagonal head atits externally exposed end to facilitate engagement with an allen wrenchor other tool to rotate screw 121 and drive locking member 120 radiallyinward to lock inner member 12 in place. In one embodiment, a pluralityof locking members 120, 122, 124 may be provided spaced around theperiphery of outer member 14 such that a surgeon can easily extend thelocking member when utilizing any one of the aforementioned toollocation holes 80, 82, 84.

Referring to FIGS. 1-9, one embodiment of end plates 20, 40 is shownwherein each end plate has a generally oblong or elliptical shape whenviewed from the end or perpendicular to the longitudinal axis 18. Asshown in FIG. 6, each end plate 20, 40 generally extends a widthdistance 90 (large outer diameter) along a long axis 92 in amedial-lateral direction and a length distance 94 (small outer diameter)along a short axis 96 in the anterior posterior direction, wherein width90 is larger than the length 94. The oblong or elliptical shape of endplates 20, 40 is designed to resemble or mimic the footprint of thevertebral body to which the end plates will engage. In this regard, endplates 20, 40 are configured to engage portions of the vertebrae in apredetermined orientation, namely with long axis 92 extending in amedial-lateral direction, to maximize contact of the superior surface ofthe end plates 20, 40 with bone.

The dimensions of end plates 20, 40 can be varied to accommodate apatient's anatomy. Typically, end plates 20, 40 may have a width betweenabout 14-32 mm (in the medial-lateral direction) and a length betweenabout 12-25 mm (in the anterior-posterior direction). In someembodiments, implants 20, 40 have a wedge-shaped profile to accommodatethe natural curvature of the spine. For example, as shown in FIG. 13,one embodiment of a wedge shape is shown wherein the end plate 130 has agradual decrease in height from an anterior side 132 to a posterior side134. In anatomical terms, the natural curvature of the lumbar spine isreferred to as lordosis. When prosthetic device 10 is to be used in thelumbar region, the angle 136 formed by the wedge should be approximatelybetween 4 degrees and 16 degrees so that the wedge shape is a lordoticshape which mimics the anatomy of the lumbar spine. In alternateembodiments, the wedge shape profile may result from a gradual increasein height from anterior side 132 to posterior side 134 to mimic thenatural curvature in other regions of the spine. Thus, in otherembodiments, angle 136 may be between about −4 degrees and −16 degrees.

As shown in FIGS. 1 and 2, a plurality of mounting holes 98 are spacedaround the perimeter of each end plate 20, 40 for receiving insertablebone engaging members 100. In one embodiment, bone engaging members 100,comprise conical spikes 102 each having a cylindrical base portion 104configured to fit within holes 98, for instance by press-fit. Inalternate embodiments, differently shaped bone engaging members 100 maybe used, or in other embodiments no bone engaging members may be used.Referring again to FIG. 2, according to one embodiment, end plates 20,40 have chamfered edges 106 around the perimeter to facilitate insertionand/or accommodate the shape of the vertebral bodies which they engage.The superior or bone engaging surface 108 of endplates 20, 40 may alsoinclude numerous types of texturing to provide better initial stabilityand/or grasping contact between the end plate and the respectivevertebrae.

The dimensions of prosthetic device 10 in accordance with the inventionmay be as follows, although the dimensions of the embodiments shown inthe figures are not critical to the invention. In one embodiment, innermember 12 may have a total height 140 of between about 13-68 mm, outermember may have a total height 142 of between about 11-64 mm, andprosthetic device 10 may be extended to a total prosthetic height ofbetween about 15-130 mm, depending on the configuration and desiredapplication.

In alternate embodiments, the length, diameter, and shape of prostheticdevice 10 may vary to accommodate different applications, differentprocedures, implantation into different regions of the spine, or size ofvertebral body or bodies being replaced or repaired. For example,prosthetic device 10 may be expandable to a longer distance to replacemultiple vertebral bodies. Also end plates 20, 40 can be sized andshaped to accommodate different procedures. For example, end plates 20,40 may be made smaller for smaller statured patients or for smallerregions of the cervical spine. In addition, it is not required that endplates 20, 40 be shaped and sized identically and in alternateembodiments they can be shaped or sized differently than each otherand/or include different bone engaging members or texturing.

Referring to FIGS. 14-25, various alternate embodiments of expandableprosthetic devices according to the present invention are shown.Referring to FIGS. 14 and 15, in one variation a central gear member 140may be positioned between the inner and outer members to engage teeth142 to facilitate expansion. Referring to FIG. 16, in another embodimentan oblong cam 160 may be used to facilitate expansion. As shown in FIG.17, an eccentric driver 170 may be used to mate with an oblong hole 172to provide expansion. As shown in FIG. 18, in another embodiment analternate worm gear 180 can be used. Referring to FIG. 19, a slot 190with a cam lock 192 may be used to expand and lock the device at acertain expansion distance. Referring to FIGS. 20 and 24, in otherembodiments, a scissor jack 200 and threaded screw 202 may be used tofacilitate expansion. As shown in FIG. 24, a wedge 204 may be used toengage the scissor jack 200. Referring to FIGS. 21 and 22, alternatethreaded devices may be used to expand the prosthetic device. As shownin FIG. 21, a tapered screw 210 may be used that may be driven by adriver 212. Alternatively, as shown in FIG. 22, a simple screw threadedengagement between the inner member and outer member may used. Also aset screw 220 may be used to lock the device at a certain expansiondistance. Referring to FIGS. 23 and 25, the inner and outer members maybe shaped to ride along an inclined plane or ramp. As shown in FIG. 23,a locking wedge or ring 230 may be provided to lock the device at acertain expansion distance. As shown in FIG. 25, rollers 250 may beprovided to facilitate expansion of the device.

FIGS. 26-29 illustrates an self-locking mechanism applied to theexpandable prosthesis. As mentioned in the previous drawings, FIG. 26likewise illustrates a prosthesis having an upper and lower endplates.The upper endplate is attached to an inner member and the lower endplateis attached to the outer member. The inner member is threaded andtranslatable along the longitudinal axis. A gear member that is providedwith internal threads is utilized to translate the inner member alongthe longitudinal axis.

The self locking mechanism of the present invention is operational byhaving a lever integrated with the entire assembly in which it is fixedto the base and configured to move radially within a fixed space toengage or disengage with the gear. The lever in its it's neural positionis engaged within the notices on the inside of the gear. When theinserter is placed into the implant, the aligning portion of theinserter pushed on the lever causing it to move distally towards thecenter of the implant such that it is no longer engaged with the notchesof the gear and thus allowing the gear to spin. When the inserter isremoved, the locking lever returns to the neural position thus lockingthe gear from turning. The present locking mechanism prevents the entiremechanism from loosensing or gaining height situ. More specifically, thepresent locking mechanisms prevents the gear from turning once theheight of the implant is set.

While the invention herein disclosed has been described by means ofspecific embodiments and applications thereof, numerous modificationsand variations can be made thereto by those skilled in the art withoutdeparting from the scope of the invention as set forth in the claims.

1. An expandable prosthetic implant device for engagement betweenvertebrae, comprising: an inner member having a hollow interior portionand a threaded external portion and including a first end portionconfigured to engage a first vertebral body; an outer member having ahollow interior portion configured to coaxially receive the inner membertherein and including a second end portion configured to engage a secondvertebral body, wherein the inner and outer members are moveablerelative to each other along a longitudinal axis; a gear memberpositioned coaxial to the inner member and outer member and axiallyfixed to the outer member and freely rotatable with respect to the outermember, wherein the gear member threadedly engages the threaded portionof the inner member, wherein the implant is configured to engage thevertebrae such that first and second end portions are oriented in apredetermined alignment with respect to the first and second vertebralbodies, wherein the gear member includes a beveled top portion and abeveled perimeter from which gear teeth extend around the perimeter ofthe gear member, the gear teeth exposed to the exterior of the outersurface of the outer member and configured to be accessible by a toolmember at a plurality of angular positions around the perimeter whereinthe outer member includes a plurality of apertures arranged along thecircumference of the outer member, wherein the tool member is capable ofengaging any of the plurality of apertures, wherein the first and secondend portions are configured with chamfered edges to facilitate insertionof the implant.
 2. The device of claim 1, wherein the outer memberincludes a plurality of tool location holes for receiving a portion of atool member therein to facilitate insertion, alignment and engagement ofthe tool member with the gear teeth.
 3. The device of claim 1, whereinthe outer member includes a resiliently deformable portion for receivingthe gear member thereon.
 4. The device of claim 1, wherein the innermember, outer member, and gear member are made of a PEEK plasticmaterial.
 5. The device of claim 1, further comprising a locking memberfor fixing the inner member with respect to the outer member.
 6. Thedevice of claim 1, wherein the inner member is rotationally fixed withrespect to the outer member.
 7. The device of claim 6, wherein the innermember includes a slot and a pin extends radially inward from the outermember to engage the slot to prevent rotational movement of the innermember with respect to the outer member.
 8. The device of claim 1,wherein the first end portion comprises a first plate having a generallyoblong shape when viewed along the longitudinal axis, the first plateextending a width distance in a medial-lateral direction along a longaxis and a depth distance in a anterior-posterior direction along ashort axis, wherein the width distance is larger than the depthdistance.
 9. The device of claim 1, wherein the second end portioncomprises a second plate having a generally oblong shape when along thelongitudinal axis, the second plate extending a width distance in amedial-lateral direction along a long axis and a depth distance in aanterior-posterior direction along a short axis, wherein the widthdistance is larger than the depth distance.
 10. The device of claim 1,wherein the first and second end plates include at least one boneengaging member extending longitudinally from the end plates.
 11. Thedevice of claim 10, wherein the bone engaging members comprise metalspikes.
 12. The device of claim 8, wherein the first end portion has athickness in the longitudinal direction and the thickness is variable inthe anterior-posterior direction along the short axis.
 13. The device ofclaim 12, wherein the thickness varies gradually in theanterior-posterior direction such that the first end portion defines ageneral wedge-shaped profile.
 14. The device of claim 12, wherein thefirst end portion extends in the anterior-posterior direction from ananterior side to a posterior side and the first end portion has a firstthickness at an anterior side and a second thickness at a posteriorside, wherein the first thickness is greater than the second thickness.15. The device of claim 14, wherein the first end portion includes abone engaging surface and a plane tangent to the bone engaging surfaceintersects a plane normal to the longitudinal axis at a first angle. 16.The device of claim 15, wherein the first angle is between about −16degrees and about 16 degrees.
 17. The device of claim 9, wherein thesecond end portion has a thickness in the longitudinal direction and thethickness is variable in the anterior-posterior direction along theshort axis.
 18. The device of claim 17, wherein the thickness variesgradually in the anterior-posterior direction such that the second endportion defines a general wedge-shaped profile.
 19. An expandableprosthetic implant device for engagement between vertebrae, comprising:an inner member having a hollow interior portion and a threaded externalportion and including a first end portion configured to engage a firstvertebral body; an outer member having a hollow interior portionconfigured to coaxially receive the inner member therein and including asecond end portion configured to engage a second vertebral body, whereinthe inner and outer members are moveable relative to each other along alongitudinal axis; a gear member positioned coaxial to the inner memberand outer member and axially fixed to the outer member and freelyrotatable with respect to the outer member, wherein the gear memberthreadedly engages the threaded portion of the inner member, a lockingmember configured to protrude radially inward from the outer member toengage the external surface of the inner member. wherein the implant isconfigured to engage the vertebrae such that first and second endportions are oriented in a predetermined alignment with respect to thefirst and second vertebral bodies, wherein the gear member includes abeveled top portion and a beveled perimeter from which gear teeth extendaround the perimeter of the gear member, the gear teeth exposed to theexterior of the outer surface of the outer member and configured to beaccessible by a tool member at a plurality of angular positions aroundthe perimeter wherein the outer member includes a plurality of aperturesarranged along the circumference of the outer member, wherein the toolmember is capable of engaging any of the plurality of apertures.
 20. Anexpandable prosthetic implant device for engagement between vertebrae,comprising: an inner member having a hollow interior portion and athreaded external portion and including a first end portion configuredto engage a first vertebral body; an outer member having a hollowinterior portion configured to coaxially receive the inner membertherein and including a second end portion configured to engage a secondvertebral body, wherein the inner and outer members are moveablerelative to each other along a longitudinal axis; a gear memberpositioned coaxial to the inner member and outer member and axiallyfixed to the outer member and freely rotatable with respect to the outermember, wherein the gear member threadedly engages the threaded portionof the inner member, wherein the implant is configured to engage thevertebrae such that first and second end portions are oriented in apredetermined alignment with respect to the first and second vertebralbodies, wherein the gear member includes a beveled top portion and abeveled perimeter from which gear teeth extend around the perimeter ofthe gear member, the gear teeth exposed to the exterior of the outersurface of the outer member and configured to be accessible by a toolmember at a plurality of angular positions around the perimeter whereinthe outer member includes a plurality of apertures arranged along thecircumference of the outer member, wherein the tool member is capable ofengaging any of the plurality of apertures, wherein the gear membercomprises a cylindrical cutout extending around an inner wall tocooperatively receive a lip of the outer member.